Transducers, such as actuators and sensors that perform conversion between mechanical energy and electric energy and speakers and microphones that perform conversion between acoustic energy and electric energy are known. In order to form a highly flexible, compact, and lightweight transducer, polymer materials such as dielectric elastomers are useful.
For example, a flexible actuator can be formed by arranging, on both sides in the thickness direction of a sheet-shaped dielectric layer formed of a dielectric elastomer, a pair of electrodes whose electric resistance does not easily increase even when the electrodes expand and contract. In actuators of this kind, when a voltage applied between the electrodes increases, an electrostatic attraction between the electrodes increases. The dielectric layer interposed between the electrodes is thereby compressed in the thickness direction, leading to a reduced thickness of the dielectric layer. When the film thickness decreases, the dielectric layer accordingly expands in a direction parallel to the electrode surfaces. On the other hand, when the voltage applied between the electrodes is reduced, the electrostatic attraction between the electrodes decreases. A compressive force against the dielectric layer in the thickness direction thereby decreases, and the film thickness increases due to the elastic restoring force of the dielectric layer. When the film thickness increases, the dielectric layer accordingly contracts in a direction parallel to the electrode surfaces. The actuator thus expands and contracts the dielectric layer, thereby driving a member to be driven.
A force and a displacement output from the actuator are determined by the magnitude of the applied voltage and the dielectric constant of the dielectric layer. In other words, the larger the applied voltage and the dielectric constant of the dielectric layer, the larger the generative force and displacement of the actuator. For this reason, materials for use in the dielectric layer include silicone rubber, which has high resistance to dielectric breakdown, and acrylic rubber, nitrile rubber, or the like, each having a high dielectric constant (see, for example, Patent Documents 1 and 2).